1. Field of the Invention
The present invention relates to a vibrating gyroscope, and, more particularly, to a vibrating gyroscope that is applied to a navigation system which detects a position of a mobile by detecting its rotational angular velocity and guides it properly, a system for damping a vibration such as a device for protecting an unsteady hold which detects a rotational angular velocity due to an external vibration such as a hand vibration and damps it properly, or the like.
2. Description of the Prior Art
FIG. 11 is a circuit diagram showing an example of a conventional vibrating gyroscope. The vibrating gyroscope 1 includes a piezoelectric vibrator 2.
The piezoelectric vibrator 2 includes a regular triangular prism-shaped vibrating body 3, and on substantially center portions of three side faces of the vibrating body 3, three piezoelectric elements 4a, 4b and 4c are formed, respectively. In the piezoelectric vibrator 2, when similar driving signals are applied to, for example, the two piezoelectric elements 4a and 4b, the vibrating body 3 bends and vibrates in a direction perpendicular to a main surface of the piezoelectric element 4c. When no-rotation, similar detecting signals are obtained from the piezoelectric elements 4a and 4b. When a rotational angular velocity is applied to the piezoelectric vibrator 2 about a center axis of the vibrating body 3, the bending and vibrating direction of the vibrating body 3 is changed by a Coriolis force, and detecting signals corresponding to the rotational angular velocity are obtained from the piezoelectric elements 4a and 4b. In this case, corresponding to the rotational angular velocity, for example, a voltage of the detecting signal from one piezoelectric element 4a becomes larger, and a voltage of the detecting signal from the other piezoelectric element 4b becomes smaller.
The piezoelectric element 4c of the piezoelectric vibrator 2 is connected to an input terminal of an oscillation circuit 5 consisting of, for example , an amplifier. An output terminal of the oscillation circuit 5 is connected to ends of two resistors 6a and 6b, and the other ends of the resistors 6aand 6b are connected to the piezoelectric elements 4a and 4b, respectively. The piezoelectric elements 4a and 4b are connected to a non-inverting input terminal and an inverting input terminal of a differential amplifier circuit 7, respectively.
Accordingly, in the vibrating gyroscope 1, by an output signal from the differential amplifier circuit 7, it can be detected that a rotational angular velocity is not applied thereto, or a rotational angular velocity applied thereto can be detected.
However, in the vibrating gyroscope 1, when a resonance characteristic of the piezoelectric vibrator 2 is shifted by changing an atmospheric temperature or environment, there is a case where each detecting signal having a drift component besides the signal corresponding to the rotational angular velocity is obtained from the piezoelectric elements 4a and 4b.
Since the detecting signals are applied to the non-inverting input terminal and the inverting input terminal of the differential amplifier circuit 7, particularly when a rotational angular velocity is not applied to the vibrating gyroscope 1, a non-zero signal is obtained from an output terminal of the differential amplifier circuit 7, so that an offset change (drift) is generated. Thus, there is a problem where it can not be detected by the output signal from the differential amplifier circuit 7 that a rotational angular velocity is not applied to the vibrating gyroscope 1.